Deep Foundations
Introduction
Deep foundations are a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does, to a subsurface layer or a range of depths. A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.
Types of Deep Foundations
There are different types of deep foundations including pile foundations, drilled shafts, caissons, and others.
Pile Foundations
A pile foundation consists of piles that are installed into the ground and then filled with concrete. Piles can be made of wood, concrete, or steel. The type of pile used depends on the ground conditions and the loads to be supported.
Drilled Shafts
Drilled shafts, also known as caissons, drilled piers or bored piles, are constructed by drilling a deep hole into the ground, and then filling it with concrete and reinforcing steel. They are used when large loads are to be supported, and the soil is too soft or loose to support a standard pile.
Caissons
Caissons are another type of deep foundation and are used when the soil is soft or when it's water-bearing. They are constructed by placing a large, hollow tube into the ground, and then filling it with concrete. Caissons are often used in the construction of bridge piers.
Design Considerations
The design of a deep foundation involves many factors, including the type and weight of the structure to be supported, the soil conditions at the site, the presence of water, and the cost and availability of materials. The design process typically involves geotechnical, structural, and construction considerations.
Geotechnical Considerations
Geotechnical considerations involve understanding the properties of the soil and rock at the site, including its strength, compressibility, and permeability. This information is used to determine the type of foundation that is most suitable, and the depth to which it needs to be driven or drilled.
Structural Considerations
Structural considerations involve understanding the loads that will be applied to the foundation, including the weight of the building, the loads from wind and earthquakes, and any other loads that may be applied. This information is used to design the foundation to have sufficient strength and stability.
Construction Considerations
Construction considerations involve understanding the methods and equipment that will be used to install the foundation, and the effects that the construction process will have on the surrounding soil and structures.
Construction Methods
The construction of deep foundations involves a number of methods, including driving, drilling, and jetting. The choice of method depends on the type of foundation, the soil conditions, and the loads to be supported.
Driving
In the driving method, a pile is driven into the ground using a pile driver. This machine raises a weight and then drops it onto the top of the pile, driving it into the ground.
Drilling
In the drilling method, a hole is drilled into the ground, and then a pile or shaft is placed into the hole and filled with concrete.
Jetting
In the jetting method, a high-pressure jet of water or air is used to loosen the soil, and then a pile or shaft is inserted into the loosened soil.
Maintenance and Inspection
Deep foundations require regular inspection and maintenance to ensure their continued performance. This can involve visual inspection, testing, and monitoring.